Imageable element and composition comprising thermally reversible polymers

ABSTRACT

The present invention also includes an imageable element, comprising a substrate and a thermally imageable composition comprising a thermally sensitive polymer which exhibits an increased solubility in an aqueous developer solution upon heating. The thermally sensitive polymer includes at least one covalently bonded unit and at least one thermally reversible non-covalently bonded unit, which includes a two or more centered H-bond within each of the non-covalently bonded unit. The present invention also includes a method of producing the imaged element. The present invention still further includes a thermally imageable composition comprising comprising a thermally sensitive polymer according to the present invention and a process for preparing the thermally sensitive polymer, which is a supramolecular polymer. The process includes contacting a hydrocarbyl-substituted isocytosine and a diisocyanate to produce a mono-adduct and contacting the mono-adduct and a polyfunctional material to produce the supramolecular polymer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an imageable element comprisinga substrate and a thermally imageable composition coated on a surface ofthe substrate. The thermally imageable composition comprises a thermallysensitive polymer, which comprises at least one covalently bonded unitand at least one thermally reversible non-covalently bonded unit, whichincludes a two or more centered H-bond within each non-covalently bondedunit. More particularly, the present invention relates to a thermallysensitive supramolecular polymer prepared from a hydrocarbyl-substitutedisocytosine, a diisocyanate and a polyfunctional material such asphenolic resin, acrylic resin, polyester resin and polyurethane resin.

[0003] 2. Description of the Prior Art

[0004] WO 98/14504 discloses a supramolecular polymer containingmonomeric units, which in pairs, form at least 4 H-bridges with oneanother. The article in J. Org. Chem., 53, 5787-9 (1988) disclosesbifunctional compounds that can associate into polymers or oligomers by2-center H-bond units. Supramolecular polymers based on 3-center H-bondunits are disclosed in Macromolecules, 28, 782-83 (1995). None of theabove references discloses the use of these polymers in thermal imaging.

[0005] EP 969 966 discloses phenolic polymers together with anon-photosensitive solubility inhibitor which provides acceptor sitesfor H-bonding and EP 985 166 discloses the corresponding methods. Thepresent invention is directed to a supramolecular polymer havingnon-covalent interactions, such as H-bonding, as an integral part of thepolymer structure. The H-bonding in the present invention is not betweena H-donor polymer and a solubility inhibitor having H-acceptor sites,but is an integral part of the polymer structure.

[0006] WO 99/01795 discloses phenolic polymers, which are modified withgroups that provide acceptor sites for H-bonding with other phenolicpolymers. The present invention is directed to a supramolecular polymerhaving non-covalent interactions as an integral part of the polymerstructure.

[0007] An article by B. J. B. Folmer et al., Advanced Materials, Vol. 12(No. 12), pages 874-878 (2000), discloses supramolecular polymermaterials. The article does not disclose polymers derived frompolyfunctional materials, such as, polyfunctional phenolic resin,acrylic resin, polyester resin or polyurethane resin, nor does itdisclose the use thereof in thermal imaging.

SUMMARY OF THE INVENTION

[0008] The present invention includes an imageable element comprising asubstrate and a thermally imageable composition according to the presentinvention coated on a surface of the substrate. The thermally imageablecomposition according to the present invention comprises: a thermallysensitive polymer which exhibits an increased solubility in an aqueousdeveloper solution upon heating, said thermally sensitive polymercomprising: at least one covalently bonded unit; and at least onethermally reversible non-covalently bonded unit, which includes a two ormore centered H-bond within each non-covalently bonded unit.

[0009] The present invention further includes a method of producing animaged element. The method comprises the steps of providing an imageableelement comprising a substrate and a thermally imageable compositionaccording to the present invention coated on a surface of the substrate;exposing the imageable element to thermal radiation to produce imagewiseexposed regions; and contacting the exposed imageable element and adeveloper within a period of time after the exposing step to remove theexposed regions and thereby produce the imaged element.

[0010] The present invention still further includes a process forpreparing a supramolecular polymer. The process comprises contacting ahydrocarbyl-substituted isocytosine and a diisocyanate to produce anisocytosine/isocyanate mono-adduct; and contacting theisocytosine/isocyanate mono-adduct and a polyfunctional materialselected from the group consisting of: polyfunctional phenolic resin,acrylic resin, polyester resin, polyurethane resin, and a combinationthereof, at a temperature and for a period of time sufficient to producethe supramolecular polymer. In addition to the thermally imageablecomposition, the present invention includes a monomer represented by theformula:

[0011] wherein each R¹ and R² is independently selected from the groupconsisting of: hydrogen and hydrocarbyl; Y is a hydrocarbylene derivedfrom a diisocyanate represented by the formula Y(NCO)₂; R³ is a phenolicresidue derived from a polyfunctional phenolic resin represented by theformula R³(OH)_(n); and n is at least 1.

[0012] The present invention also includes a supramolecular polymerderived from monomers represented by the formula:

[0013] wherein each R¹ and R² is independently selected from the groupconsisting of: hydrogen and hydrocarbyl; Y is a hydrocarbylene derivedfrom a diisocyanate represented by the formula Y(NCO)₂; R³ is a phenolicresidue derived from a polyfunctional phenolic resin represented by theformula R³(OH)_(n); and n is at least 1.

[0014] The present invention further includes an isocytosine/isocyanatemono-adduct in a monomeric or quadruple hydrogen bonded dimeric form.The monomeric form of the isocyanate mono-adduct can be represented bythe formula:

[0015] wherein each R¹ and R² is independently selected from the groupconsisting of: hydrogen and hydrocarbyl and Y is a hydrocarbylenederived from a diisocyanate represented by the formula Y(NCO)₂, thediisocyanate being selected from the group consisting of isophoronediisocyanate, methylene-bis-phenyl diisocyanate, toluene diisocyanate,hexamethylene diisocyanate, tetramethylxylylene diisocyanate, dimersthereof, adducts thereof with diols, and mixtures thereof.

[0016] The present invention still further includes anisocytosine/isocyanate bis-adduct in a monomeric or quadruple hydrogenbonded polymeric form. The monomeric form of the bis-adduct can berepresented by the formula:

[0017] wherein each R¹ and R² is independently selected from the groupconsisting of: hydrogen and hydrocarbyl and Y is a hydrocarbylenederived from a diisocyanate represented by the formula Y(NCO)₂.

[0018] In the present invention, the image areas are reinforced withstrong two or more centered H-bond links. Therefore, the image areasexhibit long press life and increased resistance to press chemicals whencompared with the systems of the prior art, which include relativelyweak single H-bond units. Thus, the thermally reversible polymers of thepresent invention can have relatively strong bonds and provide thermalsolubilization systems that have enhanced differentiation betweenexposed and non-exposed areas. These polymers can undergo thermalsolubilization and provide a durable, non-exposed area, corresponding tothe etch resist in a PCB or to the image area in a printing plate.

[0019] The imagewise exposure and development steps of the presentinvention do not require an intermediate pre-development heating step.In addition, superior press life is achieved without the need of apost-development bake because of the strength of the two or morecentered H-bond links, such as, 4-centered H-bond units, in the imageareas. The superior press life resulting from the strongly bonded imageis unexpected for a no-preheat, digitally imaged composition.Furthermore, the inventive element of the present invention,particularly when it comprises a single layer coating composition, issimple to manufacture. Accordingly, the present invention providesthermally reversible polymers that can be used in simple and costeffective methods that are useful in thermal imaging of lithographicplates and circuit boards.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The thermally imageable composition of the present invention isuseful in digital imaging applications, including printing plates andprinted circuit boards.

[0021] Lithographic printing is based on the immiscibility of oil andwater. Ink receptive areas are generated on the surface of a hydrophilicsurface. When the surface is moistened with water and then ink isapplied, the hydrophilic background areas retain the water and repel theink. The ink receptive areas accept the ink and repel the water. The inkis transferred to the surface of a material upon which the image is tobe reproduced. Typically, the ink is first transferred to anintermediate blanket, which in turn transfers the ink to the surface ofthe material upon which the image is thereafter reproduced.

[0022] Lithographic printing plate precursors, i.e., imageable elements,typically include a radiation-sensitive coating applied over thehydrophilic surface of a support material. If after exposure toradiation, the exposed regions of the coating become soluble and areremoved in the developing process, revealing the underlying hydrophilicsurface of the support, the plate is called a positive-working printingplate. Conversely, if exposed regions of the plate become insoluble inthe developer and the unexposed regions are removed by the developingprocess, the plate is called a negative-working plate. In each instance,the regions of the radiation-sensitive layer that remain (i.e., theimage areas) are ink-receptive and the regions of the hydrophilicsurface revealed by the developing process accept water and repel ink.

[0023] The present invention is useful in positive-working printingplates and includes a thermally imageable composition comprising athermally sensitive polymer, which comprises at least one covalentlybonded unit and at least one thermally reversible non-covalently bondedunit, which includes a two or more centered H-bond in each unit.

[0024] Preferably, the thermally reversible non-covalently bonded unitis a two-, three or four-centered H-bonded unit. In one embodiment, thethermally reversible non-covalently bonded unit includes a two-centeredH-bonded unit, which comprises two 2-pyridone groups. In anotherembodiment, the thermally reversible non-covalently bonded unit includesa three-centered H-bonded unit, which comprises a cyclic imide group anda 2,6-diaminotriazine groups. In yet another embodiment, the thermallyreversible non-covalently bonded unit includes a four-centered H-bondedunit, which comprises two isocytosine groups.

[0025] The term “unit” in the context of the present invention refers toany chemical group, moiety or functionality. Examples of such unitsinclude covalently bonded units, such as those derived from novolakresins, and non-covalently bonded units, i.e., two or more centeredH-bond links, such as those derived from 4-centered H-bonded units.

[0026] Such 4-centered H-bonded units in a preferred embodiment have astructure resulting from association of the two sites capable ofquadruple hydrogen bonding, namely two isocytosine units. Theassociation of the two quadruple hydrogen bonding sites and thequadruple hydrogen bonded unit resulting therefrom, i.e., the 4-centeredH-bonded unit, is schematically represented below for the “keto”tautomer, which is one of the two possible tautomeric forms of theisocytosine ring system. The schematic representation is for anisocytosine having the substituent —CH₂CH₂CH₂—R:

[0027] The 4-centered H-bonded unit can result from the association oftwo sites that are in the “enol” tautomeric form in which the hydrogenis on the oxygen atom instead of being on the nitrogen. The “keto” and“enol” tautomeric forms of an isocytosine derivative are described andproposed structures shown in the previously cited WO 98/14504, thecontents of which are incorporated herein by reference in its entirety.Accordingly, whenever a composition of present invention is representedby the formula of the “keto” form, it should be understood that theactual compound will exist either in the “keto” or in the “enol”tautomeric forms or in a combination of the “keto” and “enol” tautomericforms.

[0028] As an example, the formation of such a 4-centered H-bonded unitaccording to the present invention resulting from a 4-centered H-bondinginteraction of two 6-methylisocytosinyl groups, each attached to a groupR, is schematically represented below:

[0029] The term “supramolecular polymer” in the context of the presentinvention refers to a polymer which derives it's polymeric propertiesthrough a combination of covalent bonds and specific secondaryinteractions, which includes hydrogen bonding, particularly two or morecentered H-bond links. Such secondary interactions provide high bondstrength and contribute substantially to the polymeric behavior.

[0030] The non-covalently bonded unit acording to the present inventionincludes at least a two-centered H-bond within each unit. Preferably,the non-covalently bonded unit includes a two, three or four centeredH-bond within each unit. H-bonds that are higher than four centered canalso be useful in the present invention.

[0031] In addition to the two or more centered H-bonding, thenon-covalently bonded unit in the thermally imageable composition of thepresent invention further includes one or more additional secondaryinteractions, such as, van der Waals associations, hydrophobicassociations, ionic associations and a combination thereof. Furthermore,in addition to the two or more centered H-bonded units, the thermallysensitive polymer itself can have additional intermolecular orintramolecular interactions, including intermolecular or intramolecularH-bonding.

[0032] To achieve developability, the thermally sensitive polymer in thethermally imageable composition must have at least one base-solublefunctional group having a pKa of less than 14. Such base-solublefunctional groups include, for example, carboxylic, sulfonic, imide,N-acyl sulfonamide and phenolic hydroxy groups.

[0033] The term “hydrocarbyl” in the context of the present inventionrefers to a linear, branched or cyclic alkyl, alkenyl, aryl, aralkyl oralkaryl of 1 to 22 carbon atoms, substituted derivatives thereof,wherein the substituent group is selected from halogen, hydroxy,hydrocarbyloxy, carboxyl, ester, ketone, cyano, amino, amido and nitrogroups. Hydrocarbyl groups in which the carbon chain is interrupted byoxygen, nitrogen or sulfur are also included in the term “hydrocarbyl”.

[0034] The term “hydrocarbylene” in the context of the present inventionrefers to a linear, branched or cyclic alkylene, vinylene, arylene,aralkylene or alkarylene of 1 to 22 carbon atoms, substitutedderivatives thereof, wherein the substituent group is halogen, hydroxy,carboxyl, hydrocarbyloxy, ester, ketone, cyano, amino, amido and nitrogroups. Hydrocarbylene groups in which the carbon chain is interruptedby oxygen, nitrogen or sulfur are also included in the term“hydrocarbylene”.

[0035] Bifunctional compounds, which can associate into an oligomer orpolymer by two centered H-bond units are disclosed in J. Org. Chem., 53,5787-9 (1988). Supramolecular polymers based on three centered H-bondunits are disclosed in Macromolecules, 28, 782-83 (1995). The contentsof these articles are incorporated herein by reference for all purposes.Representative of the compounds that can associate into an oligomer orpolymer by two centered H-bond units are bridged bipyridone derivativessuch as those disclosed in the previously incorporated J. Org. Chem.,53, 5787-9 (1988), provided that such systems have at least onebase-soluble functional group, such as, carboxylic, sulfonic, imide,N-acyl sulfonamide or phenolic hydroxy groups.

[0036] The non-covalently bonded unit in this embodiment includes abridged bipyridone derivative capable of forming a two-centered H-bond.The thermally sensitive polymer in the thermally imageable compositionaccording to the present invention includes a supramolecular polymerderived from monomers represented by the formula:

[0037] wherein each R′ and R″ can independently be H, linear, branchedor cyclic alkyl, aryl, aralkyl, alkaryl, substituted aryl, alkenyl,halogen, cyano, nitro, alkoxy, aryloxy, alkoxycarbonyl, amido, acyl,aminocarbonyl, carboxylic, sulfonic, imide, N-acyl sulfonamide orphenolic hydroxy, provided that at least one of the R′ and R″ groups iscarboxylic, sulfonic, imide, N-acyl sulfonamide or phenolic hydroxy. Acan be a bridging group, such as, alkylene, arylene, aralkylene,alkarylene, substituted arylene, —O—, —S—, NR′″, —CH═CH— or —C≡C—.Representative of the compounds that can associate by three centeredH-bond units are maleimide/styrene copolymers associated with4-vinyl-2,6-diaminotriazine/styrene copolymers, such as those disclosedin the previously incorporated Macromolecules, 28, 782-83 (1995),provided that such copolymers have at least one base-soluble functionalgroups, such as, carboxylic, sulfonic, imide, N-acyl sulfonamide orphenolic hydroxy groups.

[0038] The non-covalently bonded unit in this embodiment can be a groupcapable of forming one or more three centered H-bonds with another sameor different such group to form a three centered H-bonded pair.

[0039] In one embodiment, the thermally sensitive polymer in thethermally imageable composition according to the present inventionincludes a supramolecular polymer derived from maleimide/styrenecopolymers associated with 4-vinyl-2,6-diaminotriazine/styrenecopolymers. Terpolymers thereof are also suitable for use as thethermally sensitive polymer in the thermally imageable compositionaccording to the present invention.

[0040] The covalently bonded unit according to the present invention isderived from a polyfunctional material covalently bonded to sites thatare also bonded to the non-covalently bonded units. At least one,preferably more than one, same or different polyfunctional materials canbe bonded to such sites. The supramolecular polymer can be any polymeror resin that is capable of producing properties required for thermalimaging. For example, to achieve developability, the polyfunctionalmaterial has at least one base-soluble functional group having a pKa ofless than 14. Such base-soluble functional groups include, for example,carboxylic, sulfonic, imide, N-acyl sulfonamide and phenolic hydroxygroups. The preferred polyfunctional materials include polyfunctionalphenolic resins, acrylic resins, polyester resins, polyurethane resins,and combinations thereof. Preferably, the polyfunctional phenolic resinis a phenol/cresol novolak, polyvinyl phenol polymer, vinylphenol/hydrocarbyl acrylate copolymer or a mixture thereof.

[0041] In a preferred embodiment, the thermally sensitive polymer in thethermally imageable composition according to the present invention is asupramolecular polymer derived from monomers represented by the formula:

[0042] wherein each R¹ and R² is independently selected from the groupconsisting of: hydrogen and hydrocarbyl; Y is a hydrocarbylene derivedfrom a diisocyanate represented by the formula Y(NCO)₂; R³ is a phenolicresidue derived from a polyfunctional phenolic resin represented by theformula R³(OH)_(n); and n is at least 1.

[0043] Preferably, the polyfunctional phenolic resin is phenol/cresolnovolak, polyvinyl phenol polymer, vinyl phenol/hydrocarbyl acrylatecopolymer, and a mixture thereof. The diisocyanates that are suitablefor use in the present invention include any diisocyanates, alsoreferred to herein as “difunctional isocyanates.” Preferably, thediisocyanate is selected from isophorone diisocyanate,methylene-bis-phenyl diisocyanate, toluene diisocyanate, hexamethylenediisocyanate, tetramethylxylylene diisocyanate, dimers thereof, adductsthereof with diols, and mixtures thereof.

[0044] Because the polyfunctional phenolic resin has n functionalgroups, up to n hydroxy groups can react with an equal number ofisocyanate functional groups, each attached to a site bearing anon-covalently bonded unit. Preferably, in the above-describedsupramolecular polymer n is 1, 2 or 3.

[0045] Thus, when n=2 in the above preferred embodiment, two hydroxygroups from a polyfunctional phenolic resin react with an equal numberof isocyanate functional groups, each attached to a site bearing anon-covalently bonded unit, to produce a linear polymer in which thechain growth is the result of association of sites that are capable offour-centered hydrogen bonding to produce a quadruple hydrogen bondingunit.

[0046] When n=3, three hydroxy groups from a polyfunctional phenolicresin react with an equal number of isocyanate functional groups, eachattached to a site bearing a non-covalently bonded unit, to produce acrosslinked polymer in which crosslinking is achieved throughassociation of sites that are capable of four-centered hydrogen bondingto produce three quadruple hydrogen bonding units. Thus, the thermallysensitive polymer can be crosslinked. Preferably, such crosslinks arethermally reversible.

[0047] In another preferred embodiment, the thermally imageablecomposition of the present invention further comprises a photothermalconverter material.

[0048] The supramolecular polymer can be prepared by a processcomprising the steps of contacting a hydrocarbyl-substituted isocytosineand a disocyanate to produce an isocytosine/isocyanate mono-adduct andcontacting the isocytosine/isocyanate mono-adduct and a polyfunctionalmaterial, such as, a polyfunctional phenolic resin, acrylic resin,polyester resin, polyurethane resin, and a combination thereof, at atemperature and for a period of time sufficient to produce thesupramolecular polymer.

[0049] Preferably, the hydrocarbyl groups in the above process areindependently alkyl groups of 1 to 22 carbon atoms and the diisocyanateis isophorone diisocyanate, methylene-bis-phenyl diisocyanate, toluenediisocyanate, hexamethylene diisocyanate, tetramethylxylylenediisocyanate, dimers thereof, adducts thereof with diols, or mixturesthereof. The polyfunctional phenolic resin can be phenol/cresol novolak,polyvinyl phenol polymer, vinyl phenol/hydrocarbyl acrylate copolymer,or a mixture thereof.

[0050] The isocytosine/isocyanate mono-adduct can be in a monomeric orquadruple hydrogen bonded dimeric form having a quadruple hydrogenbonded unit. The monomeric form is represented by the formula:

[0051] wherein each R¹ and R² can independently be hydrogen andhydrocarbyl; Y is a hydrocarbylene derived from a diisocyanaterepresented by the formula Y(NCO)₂, the diisocyanate being selected fromisophorone diisocyanate, methylene-bis-phenyl diisocyanate, toluenediisocyanate, hexamethylene diisocyanate, tetramethylxylylenediisocyanate, dimers thereof, adducts thereof with diols, and mixturesthereof.

[0052] The dimeric form of the isocytosine/isocyanate mono-adduct has astructure resulting from association of the two sites capable ofquadruple hydrogen bonding, namely two isocytosine units. Theassociation of the two quadruple hydrogen bonding sites and thequadruple hydrogen bonded unit resulting therefrom, i.e., the 4-centeredH-bonded unit, is schematically represented below for a related systemin which the —Y—NCO group is replaced with the group —CH₂CH₂CH₂—R:

[0053] The isocytosine/isocyanate bis-adduct can be in a monomeric formor it can be in a quadruple hydrogen bonded oligomeric or polymericform. The quadruple hydrogen bonded oligomeric or polymeric form resultsfrom association of two sites capable of quadruple hydrogen bonding,each from a different isocytosine/isocyanate bis-adduct, to produce anoligomer or polymer having repeating units of associated quadruplehydrogen bonding units, i.e., the 4-centered H-bonded units.

[0054] The monomeric form of the isocytosine/isocyanate bis-adduct isrepresented by the formula:

[0055] wherein each R¹ and R² can independently be hydrogen andhydrocarbyl and Y is a hydrocarbylene derived from a diisocyanaterepresented by the formula Y(NCO)₂.

[0056] Reaction of 1 mole of an isocytosine derivative with 1 mole ofdiisocyanate, such as isophorone diisocyanate, produces theisocytosine/isocyanate 1:1 adduct, which will spontaneously dimerize toform a dimeric mono-adduct having a thermally reversible 4-centerH-bond. The resulting dimeric mono-adduct has free isocyanate groups oneach end. This dimeric mono-adduct can then be used to form thermallyreversible crosslinks with phenolic polymers. Any unreacteddiisocyanate, such as isophorone diisocyanate, can also crosslink thephenolic polymers, however such crosslinking is not reversible.

[0057] To avoid crosslinking by the unreacted diisocyanate, an excess ofisocytosine, i.e., about 10-20% molar excess, is preferably used. Excessisocytosine can further react with the mono-adduct, which can alsodimerize spontaneously to give a diisocyanate bis-adduct having two ormore thermally reversible 4-center H-bonds.

[0058] Using “I” for the diisocyanate and “M” for isocytosinederivative, the reactions can be illustrated as follows:

[0059] To maximize the formation of lower order adducts, isocytosine isadded slowly to the duisocyanate to ensure that an excess duisocyanateis present at the early stages of the reaction.

[0060] The present invention further comprises an imageable elementwhich comprises a substrate and a thermally imageable compositionaccording to the present invention coated on a surface of the substrate.Preferably, the surface of the substrate underlying the thermallyimageable composition is hydrophilic.

[0061] The present invention is suitable for use in single as well asmultilayer thermally imageable elements that are useful in lithographicprinting, including lithographic printing plates that can be thermallyimaged by imagewise exposure with a laser or a thermal printing head.The multilayer thermally imageable element is useful as a precursor fora lithographic printing member.

[0062] In a multilayer thermally imageable case, the element has abottom layer comprising a polymeric material which can be removed bytreatment with an aqueous alkaline solution, and a top layer comprisingthe thermally sensitive polymer which exhibits an increased solubilityin an aqueous developer solution upon heating and comprising: at leastone covalently bonded unit; and at least one thermally reversiblenon-covalently bonded unit, which includes a two or more centered H-bondwithin each of the non-covalently bonded units.

[0063] The bottom layer contains a polymeric material, such as, aterpolymer of methacrylic acid, acrylamide an d N-phenyl maleimide. Thebottom polymeric material is soluble in aqueous alkaline developer, butthe top layer is insoluble in aqueous alkaline developer. However, thetop layer becomes soluble or penetrable to the aqueous alkalinedeveloper following thermal exposure.

[0064] In addition to the thermally imageable layer, the thermallyimageable element can have additional layers, such as, an underlyinglayer. Possible functions of an underlying layer include:

[0065] (1) to enhance developability of the imagewise unexposed areas;and

[0066] (2) to act as a thermal insulating layer for the imagewiseexposed areas.

[0067] Such thermal insulating polymeric layer prevents otherwise rapidheat dissipation, for example, through the heat conducting aluminumsubstrate. This allows more efficient thermal imaging throughout of thethermally imageable layer, particularly in the lower sections. Inaccordance with these functions, the underlying layer should be solubleor at least dispersible in the developer and, preferably, have arelatively low thermal conductivity coefficient.

[0068] The thermally imageable element can further have an overlyinglayer. Possible functions of an overlying layer include:

[0069] (1) to prevent damage, such as scratching, of the surface layerduring handling prior to imagewise exposure; and

[0070] (2) to prevent damage to the surface of the imagewise exposedareas, for example, by over-exposure which could result in partialablation. The overlying layer should be soluble, dispersible or at leastpermeable to the developer.

[0071] The present invention still further includes a method ofproducing an imaged element. The method comprises the steps of providingan imageable element comprising a substrate and a thermally imageablecomposition according to the present invention coated on a surface ofthe substrate, exposing the imageable element to thermal radiation toproduce imagewise exposed regions and contacting the exposed imageableelement and a developer within a period of time after the exposing stepto remove the exposed regions and thereby produce the imaged element ofthe invention.

[0072] The developer composition is dependent on the nature of thepolymeric substance, but is preferably an aqueous composition. Commoncomponents of aqueous developers include surfactants, chelating agents,such as, salts of ethylenediamine tetraacetic acid, organic solvents,such as, benzyl alcohol, and alkaline components, such as, inorganicmetasilicates, organic metasilicates, hydroxides and bicarbonates.Preferably, the aqueous developer is an alkaline developer containinginorganic metasilicates or organic metasilicates when the polymericsubstance is a phenolic resin.

[0073] Typically, the step of exposing the imageable element to thermalradiation is carried out using an infrared laser. However, other methodssuch as visible or UV laser imaging may also be used, provided that aphotoconverter, i.e., a photothermal converter, is present. Thus, forexposure with such visible or UV radiation sources, the imageablecomposition generally includes a photothermal converting material.

[0074] The Applicants have unexpectedly discovered that despite thestrong multi-centered H-bonding, it was possible to thermally reversesuch bonding during IR laser exposure in which the pixel dwell time ofthe laser is less than 100 μs. Thermally reversing the bonding byexposing at a pixel dwell time of not more than 100 μs enables one toproduce an imaged element economically and within a short period oftime, thereby providing a significant cost advantage over methods thatrequire exposures at a pixel dwell time of more than 100 μs.Accordingly, the thermal radiation in the method of the presentinvention preferably has a pixel dwell time of not more than 100 μs.

[0075] Furthermore, despite the expected ease of reformation of strongmulti-centered H-bonding, the Applicants have discovered surprisinglythat, following exposure, it was possible to remove the exposed areaswith an aqueous developer prior to reformation of the multi-centeredH-bonded units.

[0076] A characteristic feature of this process is transiency of thermalsolubilization in that developability decreases with time followingexposure. Based on the examples, imageable elements should preferably bedeveloped within up to 1 hour, more preferably within up to 30 minutes,most preferably within up to 10 minutes following exposure. For example,in the case of infrared laser imaging, the period of time between thesteps of exposing and treating with a developer is preferably less thanabout 10 minutes.

[0077] The method of the present invention can be used in one or twolayer systems. In the two layer systems, the bottom layer is soluble ordispersible in a developer, whereas the top layer is insoluble in thedeveloper. Imagewise thermal exposure of such composite layer increasesthe rate of removal of the exposed areas of both layers. The rate ofremoval of the exposed areas can be increased by enhanced rate ofdissolution or dispersibility of the bottom layer and by enhancedpermeability of the top layer. The supramolecular polymers of thepresent invention can be used in the top layer.

[0078] The thermally imageable composition of the present invention isuseful in digital imaging applications, including printing plates andprinted circuit boards.

SYNTHETIC ROUTE

[0079] The synthetic route describes in detail the synthesis of “RESINA”. Further syntheses were undertaken to produce “RESIN B” and “RESIN C”as described in table A.

[0080] Synthesis of the Qadruple Hydrogen Bonding Entity (QHBE)

[0081] Stage 1

[0082] Into a 250 ml flask were added 100 g of dried tetrahydrofuran(THF) and 13.78 g (0.11 mole) of dried 6-methylisocytosine. To thismixture was added 22.24 g (0.1 mole) of isophorone diisocyanate and theflask sealed from atmospheric moisture with a conical stopper. Themixture was left at ambient temperature for five days. The resultingmixture represented 0.1 mole of the quadruple hydrogen bonding entity,which would then be reacted with polymers containing phenolic —OHfunctionality (see Science, 278, 1601-1604 (1997) and in J. Polym. Sci.,Par A: Polym. Chem., 37, 3657-3670 (1999).

[0083] Stage 2

[0084]110.75 g of Bakelite resin LB6564 was dissolved into 400 g ofdried tetrahydrofuran (THF) in a 1 litre flask and 40% of the stage 1mixture (0.04 moles of QHBE) added slowly with stirring. Slow stirringwas continued for 1-2 days at ambient temperature. The mixture wastested for isocyanate functionality using FT-IR. The reaction wasconsidered to be complete when the presence of an isocyanatefunctionality could no longer be detected by Infrared Spectroscopy (IR).

[0085] Chemical Reactions

[0086] Preparation of QHB-Functional Phenolic Resin

[0087] The QHB-functional phenolic resin and quadruple H-bonded unitresulting therefrom are represented schematically below. Phenolicshaving 2 QHB units will undergo chain extension, whereas phenolicshaving 3 or more QHB units are capable of undergoing crosslinking.

[0088] The QHB group can form a four centered H-bond as shown below:

[0089] Isolation of the QHB Polymer

[0090] The product was isolated by precipitation into water. The mixturewas slowly poured as a thin stream into 5 litres of vigorously stirreddistilled water using a Silverson/Rotamix mixer. Initially, the productprecipitated as a sticky viscous mass, but tended to harden and crumblewith further stirring as the tetrahydrofurane (THF) was extracted fromthe polymer. The aqueous phase was decanted and replaced with freshwater and left over-night. The mixture was again vigorously stirred toform a fine precipitate, which was washed with water while beingfiltered, using a Buchner funnel. The damp cake was crumbled into adrying tray and dried at 40° C. until constant weight was obtained.TABLE A Resin LB6564 Lyncur M(S-1) Lyncur CBA Phenolic Resin (equiv. wt)116.43 108.14 262.15 Phenolic Resin (equivalents) 0.9512 0.476 0.238Resin weight (g) 110.75 51.43 62.34 QHBE (moles) 0.04 0.02 0.01 QHBEweight (g) 13.91 6.954 3.477 QHBE Solvent T.H.F. T.H.F. T.H.F.PHENOL/QHBE equiv ratio 23.78 23.78 23.78 Solvent T.H.F. T.H.F. T.H.F.Solvent weight (g). 400 200 250 Yield (g). 119.7 32 46.4 Batch nameRESIN A RESIN B RESIN C

[0091] Definitions

[0092] 1. LB6564: a phenol/cresol novolak marketed by Bakelite, UK.

[0093] 2. M(S-1): Lyncur M(S-1), a polyvinylphenol polymer havingMw=1600 to 2400 and Mn=1100 to 1500, as supplied by Siber Hegner,Beckenham, UK.

[0094] 3. CBA: Lyncur CBA (PVPh-butylacrylate), a copolymer ofpolyvinylphenol having the structure:

[0095] 4. RESIN A: the resin obtained when 110.75 g of LB6565 is reactedwith 13.91 g of QHBE.

[0096] 5. RESIN B: the resin obtained when 51.43 g of M(S-1) is reactedwith 6.954 g of QHBE.

[0097] 6. RESIN C: the resin obtained when 62.34 g of Lyncur CBA resinis reacted with 3.477 g of QHBE.

[0098] 7. KF654B PINA: an IR dye as supplied by Riedel de Haan Ltd,Middlesex, UK, having the following structure:

[0099] 8. IR dye B: an IR dye having the structure:

[0100] 9. Crystal violet: basic violet 3, C.I. 42555, Gentian violet, assupplied by Aldrich Chemical Company, Dorset, UK.

[0101] 10. Oxonol Blue: a blue dye having the structure:

[0102] 11. Paris Blue: a blue pigment supplied by Kremer Pigmente,Aichstetten, Germany.

[0103] 12. Developer A: 14% wt sodium metasilicate pentahydrate inwater.

[0104] 13. Developer B: 0.2M NaOH in water.

[0105] 14. Copper substrate A: double sided copper laminate of overallthickness 254 microns, having copper cladding 18 microns thick on eachside of an insulating substrate, catalogue number N4105-2, 0.008, H/HTHE, as supplied by New England Laminates (UK) Ltd of Skelmersdale, UK.The copper substrate is then brush grained using a mechanical grainer,stock number 4428, supplied by PCB machinery Ltd, Haslingden,Rossendale, UK, rinsed with distilled water for 10 seconds and allowedto air dry, prior to coating.

[0106] 15. Etching solution A: Ferric chloride hexahydrate crystals,catalogue no. 551-227 as supplied by RS components, Corby, UK.

[0107] 16. Stripper A: Catalogue no. 690-855 as supplied by RScomponents.

[0108] Plate Examples and Press Test Result

[0109] Formulation A and B solution concentrations were selected toprovide the specified dry film compositions with coating weights of 2g/m² after thorough drying, at 100° C. for 90 seconds in a Mathis oven.In each case the substrate used was an aluminum sheet that had beenelectrograined and anodised and post-anodically treated with an aqueoussolution of an inorganic phosphate. The coating solutions were coatedonto the substrate by use of a wire wound bar.

[0110] For formulation A, RESIN A (see Table A) and IR dye B were usedin the ratio of 98:2 (w:w). For formulation B, Paris Blue, and RESIN A(at a ratio of 1:4, w:w) were ball milled together for 4 days such thatthe dispersed mill base had a solids content of 30 wt % in1-methoxypropan-2-ol and a particle size of <10 microns as determined bygrind gauge. Thus, the formulation B coating was prepared as a solutionon 1-methoxypropan-2-ol. Formulation A B Parts by Weight RESIN A 98 80IR dye B  2 Paris Blue 20

[0111] The precursors were imaged using an internal test pattern, on aCreo Trendsetter at an imaging energy density of 250 mJ/cm². They werethen processed using a Kodak Polychrome Graphics Mercury Mark Vprocessor containing developer A at 22.5° C. at a process speed of 750mm/min.

[0112] Performance was assessed by comparing actual screen densitieswith expected densities using a Gretag D19C densitometer (available fromColour Data Systems Ltd, The Wirral, UK)

[0113] Density Results Actual Dot Readings/% Expected Dot FormulationFormulation Readings/% A B  2  2  1  5  6  5 10 10 10 20 21 20 30 31 3040 40 40 50 51 50 60 57 59 70 72 69 80 81 79 90 92 90 95 97 95

[0114] The printing forms were press tested on a Heidelberg Speed Master52 printing press, using Duo laser 80 g paper, Gibbons Geneva A1 colourink and a standard fount solution (comprising 87% water, 10.5% isopropylalcohol and 2.5% Goldfount surfactants). Each printing form ran cleanly,with no inking in background areas. Density tests were carried out onthe solid image areas (100% screen areas) at a range of runlengths.Formulations A and B maintained 100% screen density beyond 23,500impressions and the plates ran cleanly on press. There was no evidenceof coating failure throughout the printing test.

[0115] Latent Image Stability

[0116] Coating formulation C was prepared as a solution in1-methoxypropan-2-ol. The solution concentration was selected to providethe specified dry film composition of 2% IR dye B and 98% RESIN A with acoating weight of 2 g/m² after thorough drying at 100° C. for 90seconds. The precursor was then imaged using an internal test patternwith 100% coverage, on a Creo Trendsetter 3244 at an imaging energydensity of 220 mJ/cm². Next, separate samples of this precursor were cutup and the time between imaging and developing was increased (0, 1, 2, 3and 4 hours). Additional samples were stored at elevated temperature(40° C.) for 0, 4 and 21 hours. Samples were then processed using aKodak Polychrome Graphics Mercury Mark V processor containing developerA at 22.5° C. at a process speed of 750 mm/min. In this way, the latentimage stability of the formulation was evaluated using a Gretagdensitometer.

[0117] Latent Image Stability Results, Room Temperature Storage Timebetween imaging and developing/hours Formulation C 0 1 2 3 4 Expecteddot Actual dot readings/% readings/% 0 0 62 70 86 96

[0118] Latent Image Stability Results, 40° C. Storage Formulation C Timebetween imaging and developing/hours 0  4  21 Expected dot Actual dotreadings/% readings/% 0 0 100 100

[0119] Developer Resistance Tests

[0120] The solution concentrations were selected to provide thespecified dry film compositions with coating weights of 2 g/m² afterthorough drying, at 100° C. for 90 seconds in a Mathis oven. In eachcase the substrate used was an aluminum sheet that had beenelectrograined and anodised and post-anodically treated with an aqueoussolution of an inorganic phosphate. The coating solutions were coatedonto the substrate by use of a wire wound bar. Formulation D E F Partsby Weight RESIN A 98 98 100 IR dye B  2 Oxonol  2 Blue Formulation G H IParts by Weight RESIN B 98 98 100 IR dye B  2 Oxonol  2 Blue FormulationJ K L Parts by Weight RESIN C 98 98 100 IR dye B  2 Oxonol  2 Blue

[0121] Precursor samples were then developed for increasing amounts oftime at different ages, with developer A at 25° C. and a visualassessment was made of whether any coating remained, ie was the coatingresisting the developer.

[0122] Fresh Plates (Non-Imaged) Time exposed to developer/s Formulation30 60 90 120 150 180 D Coating Coating Coating Coating Some coating Allcoating visible visible visible visible left removed E Coating CoatingCoating Some All coating All coating visible visible visible coatingleft removed removed F Coating Coating Coating Coating Some coating Allcoating visible visible visible visible left removed G All coating Allcoating All coating All coating All coating All coating removed removedremoved removed removed removed H All coating All coating All coatingAll coating All coating All coating removed removed removed removedremoved removed I All coating All coating All coating All coating Allcoating All coating removed removed removed removed removed removed JAll coating All coating All coating All coating All coating All coatingremoved removed removed removed removed removed K All coating Allcoating All coating All coating All coating All coating removed removedremoved removed removed removed L All coating All coating All coatingAll coating All coating All coating removed removed removed removedremoved removed

[0123] 1 Day Old Plates, Stored at Ambient (Non-Imaged) Formu- Timeexposed to developer/s lation 120 150 180 210 240 270 300 330 360 DCoating Coating Coating Coating Some Some Some Some All visible visiblevisible visible coating coating coating coating coating left left leftleft removed E Some Some Some Some Some Some All All All coating coatingcoating coating coating coating coating coating coating left left leftleft left left removed removed removed F Coating Coating Coating CoatingCoating Some All All All visible visible visible visible visible coatingcoating coating coating left removed removed removed

[0124] 5 DAY Old Plates, Stored at Ambient (Non-Imaged) Formu- Timeexposed to developer/s lation 120 150 180 210 240 270 300 330 360 DCoating Coating Coating Coating Coating Coating Coating Coating Somevisible visible visible visible visible visible visible visible coatingleft E Coating Coating Coating Some Some Some Some Some Some visiblevisible visible coating coating coating coating coating coating leftleft left left left left F Coating Coating Coating Coating CoatingCoating Some Some Some visible visible visible visible visible visiblecoating coating coating left left left

[0125] As shown in Table A, the QHBE/phenol group equivalent ratio isabout 1/24 in these formulations. Developer resistance as a function ofQHBE level was also determined, using a series of derivatives of LB6564of different QHB level shown in the table below and compared withunmodified LB6564. QHBE:phenolic OH ratio 01:05 01:08.4 01:14 01:2401:40 LB6564 (LB6564) Resin % 98 98 98 98 98 98 IR dye B % 2 2 2 2 2 2Goldstar removal time >300 >300 >300 180 70 5 (seconds)

[0126] These results show that increasing levels of QHBE enhancedeveloper resistance. Accordingly, those skilled in the art will be ableto adjust the QHB/Resin ratio to provide an appropriate resistance forresins used in practicing the present invention, such as resins C and D.

[0127] 2-Layer Plate Example

[0128] Stage 1: Synthesis of the Quadruple Hydrogen Bonding Entity(QHBE)

[0129] Dry 6-methylisocytosine (13.78 g) (0.11 mole) and dry 2-butanone(MEK) (100 g) were charged into a 250-mL flask under N₂ atmosphere. Withthe temperature held constant at 30° C., isophorone diisocyanate (22.24g) (0.1 mole) was added dropwise, after which the temperature was raisedto 45° C. and the reaction was continued for 8 hr. The % unreacted NCOwas determined by titration to be 13.0 (11.7 theoretical), correspondingto 0.1 mole QHBE (26.5% solids).

[0130] Stage 2: Preparation of QHB-Functional Phenolic Resin

[0131] Novolac resin LB-6564 (110.8 g) and tin octoate (0.4 g) weredissolved in dry MEK in a 1-L flask, followed by the addition of QHBE(48.5 g, corresponding to 40 wt % of the stage 1 product) (0.04 mol)over a period of 1 hr with stirring. After heating under N₂ for 8 hr at80° C., all of the NCO functionality was reacted, as determined bytitration.

[0132] The MEK was removed by rotary evaporation and replaced by2-methoxyethanol (100 g). The resulting mixture was slowly poured as athin stream into distilled water (5 L), which was vigorously stirredusing a Silverson/Rotamix mixer. The resulting damp cake was dried at40° C. to provide the QHB-functional phenolic resin, UR 4309.

[0133] Plate Preparation and Evaluation

[0134] A formulation of copolymer ACR-1478 (described below) (4.25 g)and IR dye B (0.75 g), dissolved in a mixture of dioxalane (43 g),methanol (43 g) and methyl lactate (14 g) was spin coated onto alithographic aluminum substrate to provide a dry coating wt of 1.4 g/m².The plate substrate had been electrolytically grained, anodized andhydrophilized with polyvinyl phosphonic acid prior to coating.

[0135] A solution of the QHB-phenolic resin UR 4309 (3 g) in a mixtureof toluene (70 g) and 2-methoxypropanol (30 g) was spin coated onto theabove coated substrate to provide a second layer, having a dry coatingwt of 0.7 g/m².

[0136] The composite printing plate precursor was further dried for at95° C. for 3 min and imagewise exposed to a dose of 150 mJ/cm², using aCreo trendsetter 3244 at a 10W power setting. The imaged plate precursorwas processed in a PC32 processor (available from Kodak PolychromeGraphics), using Kodak Polychrome Graphics developer 956. One passthrough the processor at a speed of 2 m/min resulted in complete removalof the imagewise exposed areas and provided the imaged plate having anexcellent image and a clean background.

[0137] The image quality remained good after a second pass through theprocessor, which demonstrated good processor latitude. The plateprecursor was also shown to be white-light safe.

[0138] Preparation of Copolymer ACR-1478

[0139] Dioxalane (75 g), 95% ethanol (75 g), methacrylic acid (14.7 g),N-phenylmaleimide (59.1 g) and methacrylamide (26 g), followed bydioxalane (75 g) and ethanol (75 g), were charged into a 4-neck, 4-Lflask, equipped with a mechanical stirrer, condenser, temperaturecontroller and nitrogen purge. The reaction mixture was heated to 60°C., using a heating mantle. Azo-bis-isobutyronitrile (Vazo-64, fromDuPont) (0.135 g) was added and the reaction was maintained at 60° C.for 22 hr. After cooling to room temperature, the reaction mixture wasslowly poured onto a mixture of ethanol (1.22 kg) and distilled water(250 g) contained in a 2-gallon plastic container over a period of 45min and then stirred for 30 min. The precipitated product was filtered,re-suspended in ethanol (920 g), filtered and dried at 40° C. overnight.The ACR-1478 copolymer of methacrylicacid:N-phenylmaleimide:methacrylamide (20.9:41.6:37.4 mol %) exhibitedan acid number of about 96.

[0140] PCB Example

[0141] The coating formulation M was prepared as a solution in1-methoxypropan-2-ol/DMF (75%: 25%, v:v). The substrate used was coppersubstrate A. The coating solution was coated onto one side of the coppersubstrate by means of a wire wound bar. The solution concentration wasselected to provide the specified dry film composition with a coatingweight of 4 g/m² after thorough drying at 130° C. for 150 seconds.

[0142] Coating Formulation M Component Parts by Weight RESIN B 40 CBA,30k 57.65 Crystal violet 1 KF654B 1.35

[0143] A sample of the printed circuit board precursor was imaged on theTrendsetter 3244, using the internal test pattern, plot 0 at 400 mJ/cm².The exposed precursor was then processed by immersion in developer B for30 seconds at 20° C. At this imaging and developing condition, the 50%dots laid down by the imagesetter were complete 50% dots on thesubstrate.

[0144] The precursor was then etched (uncovered copper removed) byimmersion in the etching solution A, diluted with water (50% w:w) whichwas constantly being stirred, for between 5 and 10 minutes at 40° C. Theprecursor was then rinsed with water.

[0145] Finally, the precursor was cleaned by immersion in Stripper Adiluted with water (20% w:w) (to remove the remaining coating) at 20° C.for 60 seconds. The printed circuit board sample had a copper patternremaining that was an accurate copy of the precursor above after thedevelopment stages.

[0146] The present invention has been described with particularreference to the preferred embodiments. It should be understood thatvariations and modifications thereof can be devised by those skilled inthe art without departing from the spirit and scope of the presentinvention. Accordingly, the present invention embraces all suchalternatives, modifications and variations that fall within the scope ofthe appended claims.

What is claimed is:
 1. An imageable element comprising: a substrate; anda thermally imageable composition coated on a surface of said substrate;wherein said thermally imageable composition comprises a thermallysensitive polymer which exhibits an increased solubility in an aqueousdeveloper solution upon heating, said thermally sensitive polymercomprising: at least one covalently bonded unit; and at least onethermally reversible non-covalently bonded unit, which includes a two ormore centered H-bond within each said non-covalently bonded unit.
 2. Theimageable element of claim 1, wherein said two or more centered H-bondis a four centered H-bond.
 3. The imageable element of claim 1, whereinsaid four-centered H-bond comprises two isocytosine groups.
 4. Theimageable element of claim 1, wherein said covalently bonded unit isderived from a polyfunctional material that is soluble or dispersible inan aqueous developer solution.
 5. The imageable element of claim 1,wherein said covalently bonded unit is derived from a polyfunctionalmaterial selected from the group consisting of: polyfunctional phenolicresin, acrylic resin, polyester resin, polyurethane resin, and acombination thereof.
 6. The imageable element of claim 1, wherein saidpolyfunctional phenolic resin is selected from the group consisting of:phenol/cresol novolak, polyvinyl phenol polymer, vinylphenol/hydrocarbyl acrylate copolymer, and a mixture thereof.
 7. Theimageable element of claim 1, wherein said thermally sensitive polymercomprises a supramolecular polymer derived from monomers represented bythe formula:

wherein each R¹ and R² is independently selected from the groupconsisting of: hydrogen and hydrocarbyl; wherein Y is a hydrocarbylenederived from a diisocyanate represented by the formula Y(NCO)₂; whereinR³ is a phenolic residue derived from a polyfunctional phenolic resinrepresented by the formula R³(OH)_(n); and wherein n is at least
 1. 8.The imageable element of claim 7, wherein said polyfunctional phenolicresin is selected from the group consisting of: phenol/cresol novolak,polyvinyl phenol polymer, vinyl phenol/hydrocarbyl acrylate copolymer,and a mixture thereof.
 9. The imageable element of claim 7, wherein saiddiisocyanate is selected from the group consisting of: isophoronediisocyanate, methylene-bis-phenyl diisocyanate, toluene diisocyanate,hexamethylene diisocyanate, tetramethylxylylene diisocyanate, dimersthereof, adducts thereof with diols, and mixtures thereof.
 10. Theimageable element of claim 7, wherein n is 1, 2 or
 3. 11. The imageableelement of claim 1, wherein said thermally reversible non-covalentlybonded unit includes a two-centered H-bond, which comprises two2-pyridone groups.
 12. The imageable element of claim 11, wherein saidthermally sensitive polymer comprises a supramolecular polymer derivedfrom monomers represented by the formula:

wherein each R′ and R″ is independently selected from the groupconsisting of: H, linear, branched or cyclic alkyl, aryl, aralkyl,alkaryl, substituted aryl, alkenyl, halogen, cyano, nitro, alkoxy,aryloxy, alkoxycarbonyl, amido, acyl, aminocarbonyl, carboxylic,sulfonic, imide, N-acyl sulfonamide and phenolic hydroxy with theproviso that at least one of said R′ and R″ groups is selected from thegroup consisting of: carboxylic, sulfonic, imide, N-acyl sulfonamide andphenolic hydroxy; and wherein A is a bridging group selected fromalkylene, arylene, aralkylene, alkarylene, substituted arylene, —O—,—S—, NR′″, —CH═CH— and —C≡C—.
 13. The imageable element of claim 1,wherein said thermally reversible non-covalently bonded unit includes athree-centered H-bond, which comprises a cyclic imide group and a2,6-diaminotriazine group.
 14. The imageable element of claim 1, whereinsaid thermally sensitive polymer comprises a maleimide/styrene copolymerassociated with a 4-vinyl-2,6-diaminotriazine/styrene copolymer, withthe proviso that said copolymers comprise at least one base-solublefunctional group selected from the group consisting of: carboxylic,sulfonic, imide, N-acyl sulfonamide and phenolic hydroxy.
 15. Theimageable element of claim 1, further comprising a photothermalconverter material.
 16. The imageable element of claim 1, furthercomprising between said substrate and said thermally imageablecomposition a bottom layer that is soluble or dispersible in adeveloper.
 17. A thermally imageable composition comprising: a thermallysensitive polymer which exhibits an increased solubility in an aqueousdeveloper solution upon heating, said thermally sensitive polymercomprising: at least one covalently bonded unit; and at least onethermally reversible non-covalently bonded unit, which includes a two ormore centered H-bond within each said non-covalently bonded unit. 18.The thermally imageable composition of claim 17, wherein said thermallysensitive polymer comprises a supramolecular polymer derived frommonomers represented by the formula:

wherein each R¹ and R² is independently selected from the groupconsisting of: hydrogen and hydrocarbyl; wherein Y is a hydrocarbylenederived from a diisocyanate represented by the formula Y(NCO)₂; whereinR³ is a phenolic residue derived from a polyfunctional phenolic resinrepresented by the formula R³(OH)_(n); and wherein n is at least
 1. 19.A method of producing an imaged element comprising the steps of:providing an imageable element comprising: a substrate; and a thermallyimageable composition coated on a surface of said substrate; saidthermally imageable composition comprising: a thermally sensitivepolymer which exhibits an increased solubility in an aqueous developersolution upon heating, said thermally sensitive polymer comprising: atleast one covalently bonded unit; and at least one thermally reversiblenon-covalently bonded unit, which includes a two or more centered H-bondwithin each said non-covalently bonded unit; exposing said imageableelement to thermal radiation to produce imagewise exposed regions; andcontacting said exposed imageable element and a developer within aperiod of time after said exposing step to remove said exposed regionsand thereby produce said imaged element.
 20. The method of claim 19,wherein said thermally imageable composition comprises a photothermalconverting material.
 21. The method of claim 19, wherein said step ofexposing said imageable element to thermal radiation is carried outusing an infrared laser.
 22. The method of claim 19, wherein said periodof time is up to 1 hour.
 23. The method of claim 19, wherein saidthermal radiation has a pixel dwell time of not more than 100 μs.
 24. Aprocess for preparing a supramolecular polymer, said process comprising:contacting a hydrocarbyl-substituted isocytosine and a diisocyanate toproduce an isocytosine/isocyanate mono-adduct; and contacting saidisocytosine/isocyanate mono-adduct and a polyfunctional materialselected from the group consisting of: polyfunctional phenolic resin,acrylic resin, polyester resin, polyurethane resin, and a combinationthereof, at a temperature and for a period of time sufficient to producesaid supramolecular polymer.
 25. The process of claim 24, wherein saidhydrocarbyl is an alkyl of 1 to 22 carbon atoms.
 26. The process ofclaim 24, wherein said diisocyanate is selected from the groupconsisting of: isophorone diisocyanate, methylene-bis-phenyldiisocyanate, toluene diisocyanate, hexamethylene diisocyanate,tetramethylxylylene diisocyanate, dimers thereof, adducts thereof withdiols, and mixtures thereof.
 27. The process of claim 24, wherein saidpolyfunctional phenolic resin is selected from the group consisting of:phenol/cresol novolak, polyvinyl phenol polymer, vinylphenol/hydrocarbyl acrylate copolymer, and a mixture thereof.
 28. Asupramolecular polymer derived from monomers represented by the formula:

wherein each R¹ and R² is independently selected from the groupconsisting of: hydrogen and hydrocarbyl; wherein Y is a hydrocarbylenederived from a diisocyanate represented by the formula Y(NCO)₂; whereinR³ is a phenolic residue derived from a polyfunctional phenolic resinrepresented by the formula R³(OH)_(n); and wherein n is at least 1.